The invention relates to a process for the impact healing of inner discontinuities or defects in the sub-surface region of a cast component.
Steel castings, in particualr large castings weighing several tons, may be affected by inhomogeneities such as hot tear zones or other defects, in particualr in sub-surface region, due to uneven cooling, insufficient saturation, unfavorable casting shape or casting material inhomogeneities. Such defects, for example not completely rehealed hot tears, i.e. with small discontinuities, for example in planar arrangement, in the microstructure, can be detected for example by ultrasonic testing method. If the strength or the function of the casting is brought into doubt or reduced by such discontinuities, the casting is either lost or the discontinuities have to be eliminated.
A known process for eliminating discontinuities consists of removing the discontinuities by grinding or machining and filling the excavated areas by welding, followed by a subsequent post weld heat-treatment.
It is the object of the present invention to eliminate also large-planar discontinuities not in connection with the surface of the workpiece without having to intervene directly in the casting, that is, to create a process which can be applied externally.
The foregoing object is achieved by the process of the present invention wherein in the region of detected defects such as discontinuities an explosive charge is applied to the surface of the workpiece over the discontinuities and detonated. The workpiece can also be locally preheated, depending on material properties.